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Two MV reduced-wall TRXLPE-insulated 500-kcmil aluminum-conductor cables with encapsulated XLPE jacket were designed as replacements for the 350-kcmil copper-conductor cables with bare concentric neutral. The objective was to realize substantial cost savings on the purchase of the expensive copper-conductor cables. However, it would require an appropriate reduction of the insulation thickness of the aluminum cables in order to have the same ampacity as well as to fit into the existing 90-mm (3½″) PVC conduit. An emergency temperature test to be carried out in a duct bank containing 90° bends was chosen to evaluate the overall performance of the new cable systems. Thermal, mechanical, and electrical measurements were made in the testing. The test results were compared to those obtained previously on the 350-kcmil copper-conductor cables. [ABSTRACT FROM AUTHOR]

When a substation is fed by a combined overhead-cable transmission line, a significant part of the ground fault current flows through cable sheaths and is discharged into the soil at the transition station where cables are connected to the overhead line. Such a phenomenon, known as "fault application transfer," may result in high ground potentials at the transition station which may cause shocks and equipment damage. The scope of this paper is to present new analytic formulas which can be used for the direct calculation of the fault current transferred at the transition station and its ground potential rise as well as the substation earth current. The proposed formulas allow evaluating the influence of the main factors to the fault application transfer phenomenon and can be employed, at the preliminary design stage, to easily assess the most appropriate safety conditions to avoid dangerous effects. [ABSTRACT FROM AUTHOR]

Many models proposed in the literature to describe low-voltage power distribution networks in consumer premises as communication media require knowledge of the electrical parameters of the cables comprising these networks. These parameters are nevertheless affected by a large number of factors which may vary greatly from case to case, making it thus very difficult to achieve an exact estimation about them. In this work, a study of the electrical parameters of two cable types widely used in residential low-voltage power distribution networks is presented. Moreover, a finite-element approach is used for the verification of the results of the theoretical model concerning the series impedance per unit length of the cable type under study with respect to its normal operational conditions. [ABSTRACT FROM AUTHOR]

In this paper, a novel principle of an active power filter based on the harmonic impedance control of a transformer is proposed for high-voltage power distribution systems application. A linear transformer with multiple secondary windings is adopted. The primary winding is shunted with harmonic-producing loads, while the secondary windings are connected with inverters. The primary harmonic current is detected and then tracked by the inverters with fixed compensation coefficient. When the harmonic current compensation condition is satisfied, the transformer can really exhibit nearly zero impedance to harmonic current and primary self-impedance to fundamental current. As a result, the harmonic currents in power systems can be led to flow into the transformer branch. The operation principle, the control scheme, and the harmonic current detection method are discussed in detail. Finally, simulated waveforms and experimental results are presented to verify the effectiveness of the active power filter. [ABSTRACT FROM AUTHOR]

This work suggests recurrent neurofuzzy networks as a means to model the thermal condition of power transformers. Experimental results with actual data reported in the literature show that neurofuzzy modeling requires less computational effort, and is more robust and efficient than multilayer feedforward networks, a radial basis function network, and classic deterministic modeling approaches. [ABSTRACT FROM AUTHOR]

The magnetic hysteresis phenomenon plays an important role in the ferroresonance behavior of a transformer. however, most existing transformer models for the analysis of the ferroresonance phenomenon either ignore the hysteresis effects or represent it based on the hysteresis major loop and scale it for lower current levels. Such a modeling approach does not reflect the actual physical behavior of the magnetic core with respect to the ferroresonance phenomenon. This paper, based on Preisach theory, introduces an accurate model of hysteretic inductor to represent a single-phase transformer for the investigation of the ferroresonance phenomenon. Based on the developed model, time-domain simulation studies show that even in the case of a single-phase transformer where no magnetic coupling exists between the three-phases, all known types of ferroresonance, including fundamental, sub-harmonic, quasi-periodic and chaotic modes, may occur. The effects of hysteresis and its initial conditions, grading capacitors and transformer winding capacitance on occurrence of ferroresonance and its change of mode are also discussed. [ABSTRACT FROM AUTHOR]

Ergodic chaotic parameter modulation (ECPM) has recently been proposed as a viable modulation technique for power-line communications (PLC) due to its robustness to multipath conditions and low complexity in receiver design. While performance of ECPM has been found to be satisfactory in limited noise conditions, performance issues for other hostile challenges in the power-line environment, such as narrowband and impulsive noise, have not been extensively studied for this technique. Numerous studies have been performed on direct-sequence spread-spectrum (DSSS) modulation used in a wireless channel. The technique has been found to be well suited for a mobile environment due to its resistance to multipath fading and inherent narrowband interference suppression capability. For this study, PLC performance is investigated for both the DSSS and ECPM receiver for PLC. A signal-to-noise ratio (SNR) analysis is presented which investigates the noise-limiting properties of the power-line channel. This work provides a detailed insight to communication system performance in a power-line environment that includes the presence of significant narrowband and impulsive noise. It is concluded that while DSSS significantly outperforms ECPM in terms of bit-error rate for a Gaussian white noise-limited channel, the performance of the two techniques is similar for low SNR communication dominated by narrowband or impulsive noise. While the implementation of DSSS is more complex, ECPM is found to be less robust to low-frequency interference. [ABSTRACT FROM AUTHOR]

Power-line communications (PLC) is recognized as an alternative technology for delivering broadband services in home and small-office environments. Multicarrier modulation is one of the most effective solutions for combating the imperfections of the power-line channel. One of the technical challenges in increasing the potentiality of PLC technology is the utilization of the available spectrum when different users compete for the available resources. Due to the frequency and time-varying characteristics of the power-line network, the various users experience different channel conditions, thus the application of efficient resource allocation will increase the overall network performance. This paper addresses the problem of subchannel and power allocation for indoor PLC networks with multiple links employing power spectral density limitations, and presents an efficient multiuser loading algorithm. The proposed solution encounters both uplink and downlink traffic, guarantees a set of minimum data rates to all users, and allocates the available resources with fairness according to the channel quality of each link. We demonstrate the performance of the proposed algorithm using an illustrative example of a typical indoor network and we examine its effectiveness under various channel conditions. [ABSTRACT FROM AUTHOR]

Buried cables are often routed through short segments of conduit, and when this situation occurs, the ampacity must be reduced or the cable will overheat as a result of the high thermal resistance created at the location of the conduit. This problem is examined for extruded cables by using a finite element heat transfer software program to determine the derating in ampacity that cables in conduits must experience in order to remain below a maximum conductor temperature. The derating factors are provided as a function of conduit length, soil resistivity, burial depth and number of cables in the conduit. The results show that once the length of conduit exceeds about 20 times its outer diameter, then the ampacity of the circuit must be reduced to the value that it would have if the entire length were buried in the conduit. Factors that result in lower cable ampacities, such as high soil thermal resistivity and deeper burial depths lead to larger derating factors. [ABSTRACT FROM PUBLISHER]

This paper analyzes the influence of modeling of fault distribution along transmission line on the assessment of number and characteristics of voltage sags. The generic distribution net- work was used in all simulations. Different types of transformer winding connections were modeled and different (symmetrical and asymmetrical) types of faults were simulated. A line was selected from the previously identified area of vulnerability for a given bus and different faults having different distributions along the line were simulated. It was shown that depending on the fault distribution (uniform, normal, exponential) along the line, different numbers and characteristics of voltage sags could be expected at the selected bus. [ABSTRACT FROM AUTHOR]

Some strands were melted and broken in a 140 mm² OPGW (composite fiber-optic ground wire) in a 187 kV transmission line. It was assumed that this was caused by a lightning strike. DC arc tests simulating lightning strikes were carried out, and the melting and breaking characteristics of OPGW strands were obtained. The electric charge of the lightning strike that damaged the OPGW was estimated from the number of strands broken by the DC arc. In this paper, the DC arc test results, and the test conditions required to simulate a powerful lightning strike are described. [ABSTRACT FROM AUTHOR]

This paper presents a method employing the penalty function search algorithm to determine the LC compensator value for the optimal power factor correction in nonsinusoidal systems. The objective of the proposed method is to minimize the transmission loss while the power factor and efficiency are taken as constraints and utilized in order to solve the multiobjective optimization problem by transforming it into a single objective one. Examples show that the load nonlinearity can have a significant impact on optimal compensator sizes. [ABSTRACT FROM AUTHOR]

Lightning flashes on extremely high voltage lines are quite common and can lead to insulation breakdown or other line hardware failure causing disruption in supply. An accurate location of the site of failure will result in faster maintenance and restoration of supply. in this paper, a novel technique based on the wavelet multiresolution analysis (MRA) for locating the point of strike of a lightning overvoltage on a transmission line is presented. Lightning strikes at different points on a 400-kV transmission line of different line lengths are simulated by shifting the point of strike of the lightning impulse every S km. The Electromagnetic Transient Program (EMTP) [Microtrani is employed to generate the timedomain input signal. Daubechies eight (D8) Wavelet transform is used to analyze lightning overvoltages. The tenth level output of MRA detail signals extracted from the original signals is used as the criterion for the analysis. Extensive simulation work has been done and results indicate that the proposed scheme is very effective in locating the point of strike with reasonable accuracy. [ABSTRACT FROM AUTHOR]